The present invention relates to a photometer designed for measuring a radiation which has passed through for example a stream of hot gases. More particularly the invention relates to a photometer in which for example in a single housing is provided a source of radiation, a cuvette or chamber with charge and discharge paths for the hot gas as well as a radiation receiver set whereby particularly the gas is expected to be at elevated temperatures.
In photometers of the type to which the invention pertains one has observed a number of problems which can also be termed thermic or thermo problems because they arise on account of the elevated temperature of the measuring object, namely, a hot gas. This hot gas flows through the measuring chamber whereby for example condensation occurs of any water vapor that may be contained in the gas. This phenomenon can particularly be observed if the measuring chamber itself has a temperature below a particular value, (e.g. the dew point). Thus, care has to be taken that the temperature of the measuring chamber will remain in a particular range for example at about one hundred eighty (180) degrees C. with a tolerance of plus or minus five (5) degrees C. Alternatively it may be advisable to consider this temperature of one hundred eighty (180) degrees a minimum temperature and to prevent merely through control action the dropping of the temperature of the chamber below one hundred eighty (180) degrees.
It is now well known that the stability of a receiver in a conventional photometer is not certain and cannot be expected to be maintained if there are considerable temperature variations to which the receiver is exposed. This in effect can be observed in all kinds of receivers which have been used in photometers. In the case for example of an opto pneumatic receiver temperature variations interfere with the formation of absorption lines which then indirectly induces a temperature dependent error in the measuring results while on the other hand the sensitivity of the equipment deteriorates.
Another effect of temperature variations is to be seen in that they reduce the use-life of the receiver possibly also of the radiation source particularly because the mounting facility for theses pieces of equipment as well as any modulation structure that may be included are in fact excessively subjected to high temperatures.